The ink jet recording system is a printing and imaging method whereby fine droplets of ink are jetted under computer control and deposited on to a recording sheet such as a paper sheet to record images or letters. The ink jet recording system has features such as high speed and flexibility and is inexpensive and convenient, particularly in a case where the number of copies is relatively small. There is considerable interest in ink jet printing for various display purposes such as posters, billboards, vehicle graphics, and the like.
Hitherto ink jet prints for display purposes have been prepared by printing on to a recording medium having at least one ink-receiving layer formed on one side of a suitable support and an adhesive layer formed on the other side of the support, and a release sheet integrated thereto to cover the adhesive layer. The purpose of the receiving layer is to take up the ink rapidly and provide good image quality. The purpose of the adhesive layer is to attach the display to a suitable backing such as a support for a display or, in the case of vehicle graphics, to the body of the vehicle. The purpose of the release sheet or liner is to protect the adhesive until it is required for use. One problem with images produced using such materials is that they can be insufficiently robust to handling, and that the image or the receiving layer on which it is printed is sensitive to rubbing, scratching, and staining particularly when wet since the binder for the ink-receptive layer generally comprises water soluble or water swellable components.
Several methods of overcoming this poor robustness are known. For instance various additional coatings and treatments for ink receiving layers have been proposed, such as lacquers or varnishes which have to be applied after printing the image, thus requiring additional equipment. Another method of improving the robustness of printed images is by lamination, that is to say by covering them with a protective transparent overlay, which is commonly attached to the surface of the image receiving layer with an adhesive activated by heat, pressure, or both. This is particularly common for images intended for external display. The overlay acts as a physical protection for the image and seals it from ingress of water.
However lamination is expensive because additional materials are required together with additional handling and equipment, and there is considerable interest in finding a cheaper and simpler method of increasing the robustness of images produced using aqueous inks. We have devised an ink jet receiving material and method which provides images adequately robust for external display purposes.